WO 2009/074957 discloses a method of cosmetically treating keratinous fibers made of hair, comprising subjecting the fibers to light pulses that are emitted by a treatment apparatus and that are of duration less than or equal to 5×10−12 s. The pulses may have at least one dominant wavelength in any one of the ranges 1000 nm to 1600 nm, 700 nm to 900 nm, 350 nm to 450 nm, and 500 nm to 800 nm. The treatment apparatus may comprise a laser. Depending on the efficiencies, on the pulse durations, and on the hair, the energy density may vary in the range 0.01 J/cm2 to 10 J/cm2. The treatment is a treatment for bleaching hair, it being possible for the hair to have its natural color or to be colored artificially, the bleaching being performed with a view to the hair being dyed so as to be colored differently or with a view to it returning to its natural color. The treatment of the invention can also be used to treat hair for effects other than bleaching, e.g. for transforming the keratin (rearranging or transforming proteins, at the primary, secondary, or tertiary level), with effects, for example, on shape, softness, and/or sheen.
Hair damage, particularly due to the application of heat, is a major concern of consumers. It is therefore highly desired to style the hair without significant heating of the cuticle of hair.